What causes lug nuts to loosen up?

If it happens a second time new studs and lug nuts!

 

Ya,seems unusual.What ..Stretched threads or "reusing old lug nuts" Lol

 

I second @AModelCat on the dirt between the rims. Never had a tire loosen off after torqing when the rims are clean. Oil the threads, good certified torque wrench and never an issue.

One of our customers had a wheel off incident. Wheels were put together with mud on them, dirt fell down between the rims and got trapped between when the tires got torqued. Dirt slowly worked its way out, nuts came loose and tires went for the ditch.

 

Put lock washers on em !!!

 

Not being properly tightened and checked again after a certain amount of miles most tyre repairers will leave a notice on your truck reminding you to retention you lug nuts after say 300 miles.

 

Or soft nuts from Mexico. Thread could be bad but you should see some deformation.

 

I would think your lug nuts were over-torqued, stretching the stud treads. As the rim heats up during use, the metal expands and exerts force upon the nut and thus, backing off. You may of had some lazy tire technician hammer 600ft/lbs onto your nuts, doing the damage. Done right, the torque wrench should get at least a 1/8 turn before it "clicks". I would say your studs/nuts are finished. DO NOT CONTINUE TO DRIVE until resolved. The stretched "gap" will eventually strip the thread, start a wobble, and crack the stud off, losing both tires. In Ontario, Canada it's a $25,000 fine.

 

All hub pilot lug nuts that i’ve seen Are to be torqued 400-450 ft lbs. If you read the Manual, it’s a dry toque, only lube used is 1 drop of oil between the washer and the nut, no lube on the studs. If your tire shop put anti-seize on them they they have been overtorqued and probably pulled threads. As for them loosening, most of the incidents I’ve had, have come from tire shops. One clump of mud that didn’t get brushed off. I did have an older unit that the aluminum rims had scaled a layer of rust that had to be chipped and buffed off before they maintained torque.

 

I've always done 500 on aluminum. I think it actually shows a torque range on the nut flange.

 

Yup 450-500. Oil on the washer only. This is not rocket science stuff here. Either they wernt torqued or theres an issue. How do you know they were loose? Maybe the wheel studs were not seated in the hubs all the way? If you retorque after your drive time with the same accurate wrench they should not move. If they do something is wrong.